The present invention relates to a new type of yarn tension device capable of being used on any type of textile apparatus and, more particularly, on the machines making it possible for yarns of any type to be twisted and/or combined by twisting.
In the course of the various conversion operations which a yarn undergoes during its production, it is essential to impart as uniform and as constant a tension as possible to it. Many solutions for tension devices have been proposed hitherto for this purpose, the simplest involving simply tensioning the yarn on guide elements consisting, for example, of two disks laid one against the other and subjected to the action of a spring.
Since these solutions do not make it possible to control accurately the tension which is imparted, various proposals have been made for solving these problems.
Thus, as mentioned in the preamble of FR-A-2,145,056, it has been proposed to use tension devices which comprise, on the one hand, a pulley, the periphery of which has a friction layer and is in contact with the yarn over at least some of its circumference, and, on the other hand, means for braking said pulley. These pulley braking means consist of an eddy current brake taking the form of a motor of the asynchronous type, the rotor of which is integral with the shaft of the pulley and the stator windings of which are fed by an adjustable direct current source. Such a type of tension device which, in general terms, corresponds to the device which is the subject of U.S. Pat. No. 3,797,775, is not satisfactory, particularly in that it requires a supply of electric current and in that it is therefore necessary to have as many supply connections as there are tension devices.
The abovementioned FR-A-2,145,056 aims to overcome this disadvantage, the braking device which it describes consisting of an electric generator, the rotor of which is integral with the shaft of the pulley and the armature of which is connected to a charging resistor, the magnetic field of the generator being supplied by a permanent magnet.
The solution described in this document also allows the possibility of simultaneously ensuring the adjustment of the tension imparted by a plurality of tension devices. It has, however, the disadvantages of being costly and, above all, demanding very high accuracy in its construction.
FR-A-2,167,957 describes a solution in which braking for guiding the yarn is obtained by producing a magnet having an even number of magnetic poles, this magnet being arranged opposite a disk, the face of which is pierced with a plurality of holes and which supports the yarn guide pulley. The pulley is braked by varying the distance between the disk and the magnet.
This last solution, although making it possible to avoid the problem of electric connections, in no way makes it possible to consider simultaneously controlling all the tension devices which a textile machine having a multiplicity of identical workstations arranged side by side may comprise.